The invention relates to concepts and means for providing casting molds which permit effective heat transfer and effective lubrication over the total area of the casting mold.
Casting molds are used to shape molten metal and to extract heat from this metal to form a solid casting. These molds have two basic characteristics. The first is to extract heat to effect solidification, and the second is to provide a parting agent or lubricant to prevent adherence between the molten metal and the mold. The distribution of the parting agent or lubricant over the surface of the inner mold wall has a substantial effect on the surface quality of the solid casting, excessive amounts and concentrations of lubricant leading to pores in the surface of the casting and small amounts and concentrations of lubricant leading to a scaly casting surface.
In a continuous or semi-continuous casting the heat extraction is generally accomplished through use of water cooling on the back side of the mold lines. The cooling water is generally applied over the complete mold surface, but can also be circulated through channels machined in the body of the mold. The high thermal conductivity of the mold material provides for rapid extraction of heat from the whole internal area of the mold.
Lubrication in continuous or semi-continuous casting has been typically accomplished either by use of mold washes or by other continuous means. The mold washes generally consist of oils or greases and contain parting agents such as graphite or other non-metallic particulate. They have a short life, and thus are generally used only in semi-continuous casting operations. The continuous lubrication means requires feeding lower viscosity oils to the molten metal meniscus. Accordingly, their effectiveness is restricted to this meniscus region. Such continuous systems have also been modified for use in hot top or closed mold casting where the lubricant is fed to the meniscus-mold region.
The above known lubrication techniques have obvious disadvantages in that they have limited life or provide lubrication only at the initial point of contact between the molten metal and the casting mold. It is well known that metal-mold contact also occurs in regions away from this initial point of contact. For instance, in the casting of long freezing range alloys the inverse segregation process provides for contact between the exuding segregate and the mold, towards the exit end of the casting mold. In such instances, which are numerous, the aforementioned lubrication techniques are clearly ineffective. Just as the heat extraction means afforded by the casting mold is generally accomplished over the full mold surface, there is also a need to provide lubrication over the total mold surface.